The present invention relates to a piston rod of a vehicle height adjusting shock absorber, and more particularly, to a method of manufacturing the hollow section of the piston rod to increase the accuracy and smoothness of the hole and increase the ease of cleaning out burrs and chips from the machined hole.
In general, a vehicle is equipped with shock absorbers for improving the ride comfort during driving conditions by absorbing shocks or vibrations transferred from the road to the axle. The shock absorber is installed between an axle and the vehicle body, and the interior thereof is filled with gas or oil in order to increase damping force.
In addition to absorbing shocks to the vehicle, the shock absorbers provide the ability to keep the height of the vehicle constant regardless of the number of passengers or the baggage weight loaded. Such a shock absorber is classified as a vehicle height adjusting shock absorber.
A conventional vehicle height adjusting shock absorber includes a base shell, an inner tube installed inside the base shell, a blade, and an outer tube. The blade and the outer tube are longitudinally installed between the base shell and the inner tube. A piston rod is also installed in the inner tube, and the other end of the piston rod has an upper eye, which attaches to the vehicle body.
FIG. 1 is a sectional view of a part of a conventional piston rod, and FIG. 2 is a sectional view showing the upper eye separated from the piston rod.
As shown in FIGS. 1 and 2, in a conventional piston rod 10, a coupling recess portion 12 to be coupled with an upper eye 20 is formed in an upper end of the piston rod 10. A thread 12a is machined on an inner surface of the coupling recess portion 12. In addition, the piston rod 10 is formed with a hollow portion 14 into which a pump tube is to be inserted. Meanwhile, the upper eye 20 includes a ring portion 22 and a coupling portion 24 integrally formed with the ring portion 22. The ring portion 22 includes inner and outer rings 22a, 22b to be coupled with the vehicle body. The coupling portion 24 is coupled to the coupling recess portion 12 of the piston rod 10. The coupling portion 24 is formed with a thread 24a configured to be engaged with the thread 12a formed in the coupling recess portion 12.
The piston rod 10 is made of a solid rod, in which the hollow portion 14 and coupling recess portion 12 are formed by machining both ends of the circular rod by means of a tool such as a gun drill.
However, in case of the piston rod 10 of the conventional vehicle height adjusting shock absorber, if the hollow portion 14 is long, eccentricity between an axial of the hollow portion 14 and an axial of the piston rod 10 occurs during the process of machining the hollow portion 14. Thus, the straightness of the hollow portion 14 is deteriorated and the machined inner surface of the hollow portion 14 is not smooth. Accordingly, friction and wear can occur between the hollow portion 14 and the pump tube, and if severe, the products can be deformed.
Further, it is difficult to remove chips generated in the hollow portion 14 when it is machined, which can clog the inner channel of the shock absorber after the machining.
In addition, since the piston rod 10 is machined from a solid rod, there are problems in that the increased working time is required and the manufacturing costs are increased.